1. Field of the Invention
The present invention relates to a lead frame and production method thereof, used for manufacturing semiconductor device packages. More particularly, the present invention relates to a lead frame employed for manufacturing packages of semiconductor devices including integrated circuit (IC) devices, where the bonding strength between the lead frame and the molding compound for encapsulating the package is improved.
2. Description of the Related Art
In general, the lead frame employed for producing packages of semiconductor devices is manufactured and supplied as a strip consisting of a plurality of lead frames. The lead frame strip includes carrier rails and guide holes for supporting and holding each unit of the lead frame. Each unit of the lead frame includes a plurality of inner leads integrated with a plurality of outer leads, tie bars, and a die pad. The die pad is formed at the center of the lead frame and has an area where a semiconductor device is mounted.
In a plastic semiconductor device package, a plastic molding compound such as EMC (epoxy molding compound) forms a package body and encapsulates the device and electrical interconnections. A problem with such packages is that debonding between the lead frame and the molding compound causes failure of the package. Debonding occurs as a result of moisture penetration into the molding compound. In effect, moisture in the molding compound vaporizes during curing and test processes, which are performed under high temperature conditions, resulting in debonding of the molding compound from the lead frame.
Debonding failure becomes more serious as the semiconductor device packages are downsized. To solve the problems related to debonding failure, many efforts to improve the bonding strength between the lead frame and the molding compound have been made and include for example, the formation of dimples on the die pad of the lead frame, and the development of new molding compounds.
In an attempt to preserve bonding between the molding compound and the lead frame even under conditions of high temperature and high humidity, conventional etched lead frames are formed with dimples on the lower surface of the die pad. Also, conventional stamped frames are formed with slots or punched out areas on the die pad. The formation and the structure of dimples or slots on the die pad of lead frames is disclosed for example, in U.S. Pat. No. 4,942,452, U.S. Pat. No. 5,459,103 and U.S. Pat. No. 4,910,577.
The cost of etching dimples on the lower surface of the die pad of an etched lead frame is two to three times the cost of stamped lead frames. Moreover, when the lead frame is formed with dimples on the lower surface of the die pad, the debonding problem merely shifts from the die pad to the inner leads.
In the case of a stamped lead frame, since it is difficult to form uniform dimples, slots are usually formed. However, when slots are formed, it is difficult to attach the semiconductor device onto the die pad while bypassing the slots, and a complicated apparatus is required to attach the device. Punching the bottom surface of die pad to mimic the formation of dimples is less effective than forming the dimples themselves.
Accordingly, a need exists for a lead frame that can be mass produced and prevents debonding, but that is free from the disadvantages of conventional lead frames.